x61-stand wrote:Any idea which theme I should try? I tried a number of them, and they all basically looked alike, and none of them looked like KDE4 Oxygen.

For me, it's always been a matter of downloading themes that take my fancy and trying them. Once I settle on something I like, I write the name of the theme down. Everyone has different tastes and what might look like KDE4 to me won't necessarily look like it to you. Typing KDE4 into the theme search box might help.

I just read your post and the good replies to it. Here are my thoughts on this as well.

I don't like the dark flat colorless themes and such either in KDE Plasma 5 (Linux Mint 18.x). But, with KDE there are always many configuration options available. Of course you may have to spend some time trying them. There are a lot of Desktop Themes available and they can be customized as well, also Icon themes, color themes, cursor themes, etc...

I could not get the "Oxygen Original Plasma theme" to install, except using the archive file, the ".deb" file would not install. I had to extract the archive file and manually copy the "oxygen2" folder into the folder below, then it showed up.

A note of caution: I really liked the "Blue Tint Glass" desktop theme in Linux Mint 17.x Plasma 4, but in my Linux Mint 18.1 system using Plasma 5, it stopped my mouse from working properly, no right click options? When I switched to another theme, no problems. I guess some of the older Plasma 4 themes have not been updated well for Plasma 5.

I could not get the "oxygen-crystal-diamond" to install either, but there are many others available.

Under System Settngs -> Application Style -> Widget Style, if you select "QtCurve", then a whole bunch of custom configurations become available (works in LM17.x too), like custom scroll bars with colors.

Thanks Phd21 & minitux. I wanted to give a redux of what's going on. I'm listing instructions on how to configure a KDE4 look-alike on KDE5 starting with a clean install of KDE Linux Mint 18.2

First, installing most KDE themes from the settings panel fails. That is happening in general, not specific to this situation. Also, the KDE store is broken. You have to use Google to search for anything, otherwise you have to sort through 20 pages of results to find anything. So, I'm giving the exact links for the themes to install. Don't use the System Settings panel to install these.

Install from a Web Browser:
1) Oxygen Remixed Icons from https://store.kde.org/p/1160037 ; Go to the Files panel and select download option for the .deb file; When the dialog pops up, open with GDebi. There are pre-requisites which the installer will take care of.
2) Oxygen Original Plasma theme from https://store.kde.org/p/1162362/ ; Go to the Files panel; Click on the .deb file which should open in GDebi. This installed for me. I think the issue is that this package install bombs if you don't have all the pre-requisites installed first.

Configure:
1) Open up System Settings. You have to work through Workspace Theme, Color, Icons & Application Style to configure everything.
2) Under Workspace Theme, set Desktop Theme to Oxygen2, I use Cursor Theme DMZ(white) (It's not really Oxygen White, but I couldn't get that to install, and this one looks pretty good).
3) Under Color, select either Oxygen or Oxygen Cold (my fave).
4) Under Icons, select Oxygen Mix. Go to the Advanced tab, shut off Desktop -> Animate Icons check box (unless you like that sort of thing). I changed Emoticons to EmojiOne, but kde4 is also an option.
5) Under Application Style, change Widget Style to Oxygen. A lot of the configurability that was here in KDE4 is now missing. If you click on the Configure... button to the right, go to the Animations tab and uncheck the "Enable Animations" checkbox (unless you like that sort of thing).
6) Under Window Decorations, run "Get New Decorations", search for oxygen. Scroll down until you hit "air-oxygen". Install then apply it. This one actually installs. It's not perfect, but this looks pretty decent. I set the GNOME Applications style to also use the similar Oxygen theme & Icon themes as selected above.
7) I had this weird problem where the Widget style would keep switching back to Breeze from Oxygen. However, if I quit the System Settings instead of going back with the back arrow, the widget style remains on Oxygen.

Summary: The improved icons only work with Oxygen2. I really don't like the color scheme of the task bar & kickoff menu, I prefer Air, but if you use Air, the icons revert back to the ugly outline forms. I suppose I'll get used to it. Phd21 suggested using Widget Style QtCurve. I looked at it, and the base form isn't as good looking as Oxygen, but there are a huge number of configuration options. I wish I had time to play around with it. Hey phd21, if you have some good settings for this beast, please post or link. I'd love to check it out, but the combinations look like several hours work just to try them. I think the biggest improvement with this configuration was with the new icons and the window decorations. KDE5 (Plasma 5 for the pedantic) looks acceptable now. It's still not great, but good enough to actually install it on a work machine, which I'm going to do right now.